1. Field
This disclosure relates generally to semiconductors, and more specifically, to a method for treating a bond pad of a package substrate.
2. Related Art
Some microelectronic device packages include wire bonds for providing electrical coupling between a package substrate and an encapsulated die. Typically, a wire bond includes a piece of wire that couples a terminal on the die to a pad on the package substrate. Although the wire itself can be made of copper, the point of contact on the substrate's pad is not fabricated with bare copper since bare copper pads oxidize over time, making the resulting bonds unreliable.
To address some of these concerns, a substrate wire bonding structure may include a plating material that is deposited over a layer of copper to protect it from oxidation while enabling a metallurgical bond to be formed between the wire and the structure. Most widely used plating materials include gold. However, the use of gold on a package substrate presents a significant manufacturing cost. Also, OSPs (Organic Solderability Preservatives) have been tried as a coating to protect a copper pad from oxidizing, but this practice results in weak connections because the resulting OSP coating is too thick for reliable wire bonding because it leaves an organic residue between the wire and the pad.